1 Channel Mixer

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Zacharie Brodhacker

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Aug 5, 2024, 3:28:27 AM8/5/24

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Blackand White photography is a big topic that deserves entire books devoted to the subject. In this article we are going to explore some of the most common methods for converting a color digital image into monochrome in GIMP. What We are Trying to...

This now adds the Green channel values to the Red channel (50), increasing the total red channel values.

You can see how the red channel blows out now on her cheek and forehead (the values have reached their upper limit and are clipping).

Though, I am still not clear if I simply need to adjust the colors (not working on B&W), why I need to modify other colors in a certain channel instead that I simply just adjust RGB. As you have pointed out already:

Using the channel mixer set the blue component of the red color (blue dot in red circle) to 50.

What happened?

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Blue changed to purple as expected. But simply increasing the brightness of the red channel (because we added some of the values from the blue channel into the red channel) means that all colors will shift to red. Did that happen?

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Yes, the whole image has a reddish color cast. Look at the bottom row of what used to be grey patches - they be pink.

You will not be able to replicate the effect of adding another channel value to the Red channel (for example) by simply modifying only the Red channel Reds. That is, adjusting the blue slider in the Red channel will produce an effect that you cannot get by only modifying the red slider in that channel.

Any slider in the Red channel can only affect the R value of your output pixel. Likewise, any slider in the Green channel can only affect the G value of the output pixel, and any slider in the Blue channel can only affect the B value of the output pixel.

The RGB values you see in the Navigator panel depend on the working colorspace. If you set it to sRGB the numbers will look as expected. The default space is ProPhoto though and using it the numbers are different.

@hardywang First of all thanks for starting this topic! RGB Channels is one of my favourite tools in RT (mostly because it enables me to do some Jose Villa shooting Fujifilm 400H film magic to images by making greens bluer and by making skin tones goldener by taking blue out of red)

This would mean, since we talk about the red channel, we discuss how much red we put in each channel. So according to the above, we put all of the red channel (all the red colour there is to be worked with) into the final red output, while none of the red is added to the final blue output or green.

So the way I think of it when I do this is the following; I go to the channel that I wanna do stuff with, in this case it being blue; and then I do stuff with it, in this case add some into green, in this case adding +40 in the green section of Blue Channel.

Considering the previous comment by @Morgan_Hardwood about how making changes to colour channels, I guess I would have to cancel out the channel imbalance by also making the B: 60 (because 100-40=60).

So if I got this somewhat right, the rule of thumb is this:

When dealing with RGB Colour Channels in RawTherapee; when you look at one of them, say Red Channel, you think that this is the colour you are about to work with; and when you edit the R, G, B values within it, you think of those as where you add said channel to.

Q: Why is my output distorting when I use a custom mix?

A: The sum of the two %s in one or both channel outputs is in excess of 100%. For example, if the Left output channel had 50% of the original Left channel and 60% of the original Right channel, it would distort.

Gale

Q: Why is my output distorting when I use a custom mix?

A. The mix of the two %s in one or both channel outputs is in excess of 100%.

For example, if the Left output channel had 50% of the original Left channel

and 60% of the original Right channel, it may distort. This may even occur if

one of the %s is negative. For example, if the Left output channel had +50%

of the original Left channel and -60% of the original Right channel, it could

distort.

Q. Why do the Wide and Extra Wide setting sometimes distort?

The Channel Mixer effect has been deemed, "obsolete. " I assume because of old code, but what new effect can duplicate its features? I use this effect to accurately and easily create monochrome RGB color seperations of color footage. (As if I shot on black and white film with an R, G, or B filter.) Once I have that channel seperation I use it on a layer above with the luminosoty blending mode to add customized color punch to the color footage below. If I try to replicate this with Lumetri curves by pulling out the unwanted channels and desaturating it it does not produce the same image as the old channel mixer would. Its density is wrong, its darker and it also does not behave properly when using a blending mode. Is there an updated replacement for this or am I going to have to dynamic link to AE and use its channel mixer or suffer with the horrible realtime performance of the old effect?

If something appears in the public beta, then we'll know they have a new effect. I'm not counting on it though. At this time, you need to head over to AfterEffects if you really need the channel mixer.

But what's worse ... it takes the entire processing chain down from the normal 32-bit float to 8 bit. So when using this, use it AFTER any other effect that may touch on color. Probably use it as the last effect if possible.

Thanks for that info Neil, I suspected as much. Its really too bad that they don't keep basic utility tools up to date. They cram everything under the sun into Lumetri but it can't do a basic color separation correctly. I use the effect on its own layer so I'm not sure how/if that affects other layers? Do all layers become 8 bit if any one is 8 bit?

I would like a new channel mixer too. And they've added a few things to Lumetri over the last several years, but not that much. It's still not nearly as fully capable as SpeedGrade was when they EOLd that back in 2015. There's a lot of correction capabilities Lumetri is still missing.

I definitely NEED an up-to-date VIDEO CHANNEL MIXER to properly colorgrade the diving videos of my GoPro. Nothing in the current Lumetri pannel is close to matching as easily the results of the "obsolete" mixer. Whom should I request it in order to add my voice to yours? In 50 years instead of 1 century, we might succeed in getting it

I'm more visual than expert. The purpose was to find a quicker way to colorgrade properly diving videos that are notoriously lacking red and green. A brazilian diver called Gustavo Vier created a preset based on the Video Channel Mixer and I got inspiration from him and other youtube tutorials, with a little bit of practice and experimentations.

How big is the clip? I'm on the road (Vegas for NAB) and don't have regular wifi/internet available, I'm having to do a mobile hotspot with my phone. Though my capablities in Premiere are limited on this laptop also.

The Color Channel Mixer is still working even if it is a bit touchy and causes Premiere Pro to crash from time to time. Be aware you have to save your work on a regular basis in order to avoid loosing it.

Anyway I'm confident in the fact that Adobe will develop another up-to-date Color Channel Mixer for Premiere Pro. If not and if this fabulous tool disapear, I have to say I will loose all interest in Premiere Pro.

A brazilian guy named Gustavo Vier made available his preset on internet based on the Color Channel Mixer. I thank him every time I produce a new underwater video. You have to tune it, afterwards, sequence by sequence. To install a preset, look at youtube which is full of tutorials.

Update - I found a way around the old channel mixer for my specific needs. I created the RG&B monochrome channel mixer effects in Photoshop and saved them as individual LUTS. In Premiere Lumetri loads them and I get the same look as the old channel mixer but with full acceleration and color depth. Also less clunky than AE linked comp which was the only other current option.

When converting pictures to Black & White inPhotoshop many people, including me in the past, wouldjust select image->mode->grayscale, job done.The result was usually a bit lacking in contrast buta tweak with a curve layer would soon fix that.

I have chosen the picture on the left, not becauseI foresee a massive demand for black & white picturesof spaghetti, but because the colors are similarto those you would find in skin tones. And what dowe photograph more than anything else? People.

Below left is the result of just changing the modeto grayscale, as you can see it's a bit washed outand lacking in detail compared to the picture on theright that has been created using the channel mixer.

If you are not familiar with channels you'll findthe channels palette under the 'window' menu. Thereare three channels, one each for red, green and blue,and an RGB view, which is the one we normally see.Think of these channels as the three layers on a colorfilm, each represents the amount of it's color (red,blue and green) in the final image. Another way tolook at it is that it represents a black & whiteimage taken through a filter so that only it's colorreached the film.

As a general rule ofthumb, we want black & white images to be a bitmore contrasty than their color equivalents. Theimage below left is probably an accurate conversionfrom the color but the one on the right is more satisfying.

So, in order to increase the detailand contrast in the image, what we want is an imagemade up of more of the blue and green channels andless of the red channel. And this is exactly whatwe can do with the 'channel mixer'. Open the channelmixer, image->adjustments->channel mixer, andyou will see a window like the one below.